|Material Processed||Ag, Al, Al2O3, Au, Cr, Cu, Fe, Ge, Ni, Pt, SiO2, Ti, TiO2, Zn|
|Sample Size||6", 4", 3" and 2" wafers, Pieces|
|Gases Used||Ar, N2, O2 1%, O2 0.1%|
|Overview||General Overview: Wikipedia Sputter Deposition|
|Warning:||This page has not been released yet.|
Sputter Deposition is a physical vapor deposition (PVD) method of thin film deposition in which a high-purity source material (called a cathode or target) is subjected to a gas plasma (typically Ar.) The energetic atoms in this gas plasma collide with the target material and knock off source atoms which then travel to the substrate and condense into a thin film.
Figures of Merit
Deposition rate, usually expressed in Å/sec, is measured at the substrate using various methods. It is set using deposition time on the sputter tools
- In sputtering the deposition rate is measured for a set power and pressure. Rates can be changed by varying the power and pressure but it then needs to be characterized for the new settings.
- Stress can be moved by varying power and pressure of the deposition.
- Heating and substrate bias can affect materials deposited on the substrate.
- Deposition rates vary greatly by material (sputtering yield) and deposition method (power supply.) In general, softer metals deposit quickly using DC while harder insulating materials will have slower deposition rates using pulsed DC or RF.
Uniformity measures the variation in thickness across a substrate and is usually expressed as a percentage. Typically: (Thickness Max - Thickness Min)/Thickness Average. Uniformity is typically set by the material being deposited and the geometry of the system: throw distance, substrate rotation and deposition angle.
- In sputtering, uniformity is determined by throw distance and the shape of the deposition
- In the Denton and Lab 18 tools, smaller sources eject material from the face of a 3" target that is angled to cover around 1/2 of the substrate area. The substrate is rotated to coat the entire area. Varying the angle will vary the throw distance and change the amount deposited on the center and edge. The supplies have a set throw angle that is optimized for best uniformity.
- In the ALN tool, the wafer is centered over two targets which are larger than the substrate. Uniformity can be only be adjusted using the DC supply which raises and lowers the power to the center target.
Stress is a a measure of the force that the film exhibits on itself and the substrate. It is usually measure in mega-Pascals (MPa) with positive stress being called "tensile" and negaitve stress referred to as "compressive." Stress in thin films can affect devices and substrates as well as poorly affect adhesion and other properties. In terms of deposition parameters, stress is affected by the energy and angle of the material as it strikes the substrate.
- In sputtering, stress is determined by the vertical energy of the material as it strikes the substrate.
- Lower pressure and higher power drive stress more compressive (atoms colliding with energy and "packing into" the film, driving it compressive.) High pressure and lower power do the opposite. Very high pressure can lower the absolute stress in the film but usually this is associated with high gas inclusion which means the film quality of poor.
- Substrate bias can also add energy to the incoming atoms and drive stress compressive.
Resistivity is an electrical measurement of the characteristic of the film It can be measured on electrical structures (lengths of wiring lines) or on blanket films using the four-point probe. It is expressed in many units, typically μ-ohm-cm.
Resistivity is typically used to measure the quality of the film in terms of source purity or vacuum purity but it can be changed by altering the density of the film (pressure, power and bias during sputtering)
- In sputtering, step coverage is increased by creating more non-normal incident atoms
- Higher pressure and lower power can help step coverage at the expense of dep rate.
- Substrate Bias and Ar Etching (bias with no sputtering plasma) can sometimes be used to knock material off of via bottoms and redeposit them on sidewalls
- The LNF has 4 Sputter Deposition Tools
- The following materials can be deposited using Magnetron Sputter Deposition.
- Materials Deposited: Al2O3, ITO, Mo, Si, SiO2, Si3N4, Ta, Ta2O5, Ti, TiO2
- Lab 18-1 is a loadlocked magnetron sputter tool used for depositing metals, insulators, optical and semiconductive films. It has a variable-gated turbo pump and more sensitive gas flows that allow it to run more sensitive gas ratios (<1%) for reactive sputtering. It has a DC supply for conductive materials and RF supplies for electrically insulating materials. Deposition rates vary by material but are generally mich slower for RF depositions. The tool supports 5 materials at a time, rotated using the 18-1 Target Change Calendar
- Materials: Al,Cr,Cu,Au,Ge,Ir,Ni,NiCr,Pt,Si,Ag,Ti
- Lab 18-2 is a loadlocked magnetron sputter tool used for mostly for depositing metals. It uses DC for conductive materials and RF for electrically insulating materials. Deposition rates vary by material but are generally slower for RF depositions. The tool supports 5 materials at a time, rotated using the 18-2 Target Change Calendar
- The Denton Explorer is an open-loop 2-source magnetron sputter tool used as a Lab 18 backup for depositing metal films
AMS 2004 Aluminum Nitride Sputter Tool
- Materials deposited: AlN, Al
- The AMS tool is designed specifically for Piezoelectric AlN on 4" wafers. It is a high temperature process that works only on certain substrates with specific seeding matetrials and the handler is only designed for 4" wafers are this time.